Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Most thermostatic expansion valves are set for a superheat of

10°C

15°C

5°C

20°C

2. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

3. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Always more than unity

Always less than unity

Any one of the above

4. A thermostatic expansion valve in a refrigeration system

None of the above

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

5. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Carnot

Carnot

Reversed Rankine

6. The curved lines on a psychrometric chart indicates

Relative humidity

Dew point temperature

Wet bulb temperature

Dry bulb temperature

7. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₂ - T₁)/T₁

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

8. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

9. Which of the following cycles uses air as the refrigerant?

Carnot

Bell Coleman

Stirling

Ericson

10. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

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11. Cooling water is required for following equipment in ammonia absorption plant

Absorber

Condenser

Evaporator

Condenser, absorber and separator (rectifier)

12. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

9: 1

1: 1

1: 3

13. The capillary tube, as an expansion device, is used in

Domestic refrigerators

All of these

Water coolers

Room air conditioners

14. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

15. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Wet vapour

Superheated vapour

Dry saturated vapour

16. The boiling point of ammonia is

-33.3°C

-77.7°C

-10.5°C

-30°C

17. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Freon

Carbon dioxide

Ammonia

Brine

18. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

Zero

None of these

Positive

19. Which of the following is not a desirable property of a refrigerant?

Large latent heat

High risibility with oil

Low boiling point

Good electrical conductor

20. Rating of a domestic refrigerator is of the order of

40 tons

0.1 ton

10 tons

5 tons

Page 3 of 4

21. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Less

Unpredictable

Equally

22. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.67

0.376

0.6

23. Freon group of refrigerants are

Nontoxic and non-inflammable

Toxic

Non-inflammable and toxic

Inflammable

24. A bootstrap air cooling system has

Three heat exchangers

One heat exchanger

Four heat exchangers

Two heat exchangers

25. For obtaining high COP, the pressure range of compressor should be

High

Low

Any value

Optimum

26. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Evaporator and compressor

Condenser and receiver

Compressor and condenser

27. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

2.33

1.33

3.33

28. The freezing point of sulphur dioxide is

-56.6°C

-77.7°C

-75.2°C

-135.8°C

29. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

30. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Dew point temperature of air

Wet bulb temperature of air

Ambient air temperature

Page 4 of 4

31. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Centrifugal

Axial

Miniature sealed unit

32. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Refrigerant cooling tubes

Capillary tubes

Condenser tubes

33. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

None of these

34. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

1.25

2.15

35. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Detect liquid in vapour

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

36. Critical temperature is the temperature above which

A gas will never liquefy

A gas will immediately liquefy

Water will never evaporate

Water will evaporate

37. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

2 bar

15 bar

8 bar

38. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Involves no change in volume

Takes place at constant temperature

Takes place at constant pressure

39. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Above critical temperature

Near critical temperature of refrigerant

Much below critical temperature

40. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

Sub-cooling or under-cooling

None of these

Normal cooling

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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